This invention relates to a closure for sealing a container of draft beer or the like and for coacting with a tap for dispensing beer from the container. More particularly, the invention relates to a closure of the same general type as disclosed in Johnson, Jr. et al U.S. Pat. No. 3,410,456 and Johnson, Jr. et al U.S. Pat. No. 4,000,829.
The closures disclosed in those patents each includes a sealing plug molded of rubber or the like and formed with a central bore which receives a tapping tube for introducing pressurized gas into or withdrawing a beverage from the container. The lower end of the bore initially is sealed by a thin rubber membrane which overlies a hinged rubber flapper. As the tube is inserted into the bore, it pierces the membrane and swings the flapper downwardly. The membrane folds downwardly along and seals against the tube to prevent the beverage from escaping from the container along the outer side of the tube. When the tube is withdrawn, the hinged flapper swings upwardly and seals off the punctured membrane.
While closures of the foregoing type have enjoyed considerable commercial success, they are not without problems. One problem results from the fact that a slug of rubber is sometimes punched out of the membrane when the latter is punctured. The slug falls into the container and creates an unsightly appearance.
A second problem presented by the prior closures is that the flapper may re-seal the container too tightly after the tap has been removed from the container. If the closure is used to seal a disposable container made of P.E.T. or the like, the flappers of the prior closures establish such a tight seal that the container may burst at abnormally high pressures rather than relieving the pressure through the closure. Also, the prior closures are not capable of venting a nearly empty disposable container. If such a container is left in a lowly pressurized condition, heat (e.g., direct sunlight) could increase the pressure to such a high magnitude as to cause the container to burst.
The flappers of the prior closures also add to the cost thereof. After such a closure has been molded, it is necessary to perform a slicing operation on the lower end portion of the closure to separate the flapper from the membrane. In addition to the cost involved in the slicing operation, rigorous inspection procedures are necessary to insure that the membrane has remained intact after the slicing operation.